[css3-conditional] Clarify the definition of "literal match" in CSS.supports().

This edits in the fifth resolution in
http://lists.w3.org/Archives/Public/www-style/2012Aug/0749.html
in a clearer way.

Author: dbaron

css3-conditional/Overview.html

@@ -1283,8 +1283,12 @@ <h3 id=the-css-interface><span class=secno>7.6. </span> The <a
     arguments <var>property</var> and <var>value</var>, it must return
     <code>true</code> if <var>property</var> is a literal match for the name
     of a CSS property that the UA supports, and <var>value</var> would be
-    successfully parsed as a supported value for that property. Otherwise, it
-    must return <code>false</code>.
+    successfully parsed as a supported value for that property. (Literal
+    match means that no CSS escape processing is performed, and leading and
+    trailing whitespace are not stripped, so any leading whitespace, trailing
+    whitespace, or CSS escapes equivalent to the name of a property would
+    cause the method to return <code>false</code>.) Otherwise, it must return
+    <code>false</code>.
     <p> When invoked with a single <var>conditionText</var> argument, it must
      return <code>true</code> if <var>conditionText</var>, when parsed and
      evaluated as a <a

css3-conditional/Overview.src.html

@@ -1038,6 +1038,11 @@ <h3 id='the-css-interface'>
     When the <code title=''>supports()</code> method is invoked with two arguments <var>property</var> and <var>value</var>,
     it must return <code>true</code> if <var>property</var> is a literal match for the name of a CSS property that the UA supports,
     and <var>value</var> would be successfully parsed as a supported value for that property.
+    (Literal match means that no CSS escape processing is performed,
+    and leading and trailing whitespace are not stripped,
+    so any leading whitespace, trailing whitespace,
+    or CSS escapes equivalent to the name of a property
+    would cause the method to return <code>false</code>.)
     Otherwise, it must return <code>false</code>.
 
     <p>